Method for making a film cassette for gaseous vapor deposition

ABSTRACT

The present invention is a method for making a film cassette end plate and a film cassette comprises two end plates. The uncoated end plates are formed using one of several known plastic forming methods. The end plates are coated with an inorganic coating to impart smoothness and hardness to facilitate film handling and reduce wear. The end plates are mounted on a shaft to form a cassette.

CROSS REFERENCE TO RELATED APPLICATIONS

Subject matter disclosed herein is disclosed and claimed in thefollowing copending applications, all filed contemporaneously herewithand all assigned to the assignee of the present invention:

Film Cassette For Gaseous Vapor Deposition (CL-4584);

Loaded Film Cassette For Gaseous Vapor Deposition (CL-4818);

Apparatus For Gaseous Vapor Deposition (CL-4821);

Apparatus and Method For Loading A Film Cassette For Gaseous VaporDeposition (CL-4820); and

Apparatus and Method For Unloading A Film Cassette For Gaseous VaporDeposition (CL-4822).

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to a film cassette for supporting a filmsubstrate during a gaseous vapor deposition process, to a method formaking the cassette, to an apparatus for depositing one or morematerials on a substrate using a gaseous vapor deposition process, andto apparatus and methods for loading and unloading the cassettes.

2. Description of the Art

In order to manufacture affordable thin film photovoltaic modules anindustrial length roll of an ultra-barrier film (on the order of 10 to200 meters or more) and about 350-1650 mm in width is needed. Anacceptable ultra-barrier film should be able to limit the entry of watervapor and/or oxygen into the photovoltaic layer of a thin filmphotovoltaic module to a water vapor transmission rate of less than5×10⁻⁴ g-H₂O/m²-day. Entry of water vapor or oxygen is deleterious sinceit tends to rapidly destroy the photovoltaic layer of the module.

Currently, it is possible using a roll-to-roll process to manufacturecoated films (such as used for bags of comestible snack products) thathave a water vapor transmission rate only as low as 10⁻³ g-H₂O/m²-day.Attempts to use the available roll-to-roll technology to manufactureindustrial length rolls of ultra-barrier film for organic light emittingdiodes (OLED's) proved unsuccessful, falling far short of the threshold(5×10⁻⁴ g-H₂O/m 2-day units) necessary for a film to be effective as anultra-barrier.

In these previous attempts at roll-to-roll manufacturing of coatedultra-barrier film for OLED's a material was deposited onto the surfaceof a film substrate using chemical or gaseous vapor deposition, such asthe process known as atomic layer deposition. During previousroll-to-roll manufacturing attempts, the process rollers contact againstthe full surface of the substrate, producing surface scratches on thesubstrate. Moreover, the substrate undergoes significant bending as itis conducted from one roller to another, producing additional cracksthrough the deposited barrier coating. Such scratches, abrasions,creases or cracks destroy the ability of any deposited barrier coatingto prevent moisture or oxygen ingress.

Film cassettes able to support lengths of silver halide film (typicallybetween 35 to 100 mm in width) during chemical batch processingdevelopment are known in the photographic arts. Such cassettes typicallysupport the film being developed in a spiral fashion. In a spirallywrapped cassette the film being processed is held edgewise in the spiralgroove of the cassette, without the surface of the film being contacted.Representative of such prior art film cassettes are a metallic cassettesold by Hewes Photographic Equipment Manufactures, Bedfordshire,England, and a plastic cassette sold by Paterson Photographic Limited,West Midlands, England.

There are, however, difficulties in scaling either metal wire (stainlesssteel) or commonly available plastic spiral wound cassettes for use witha film having a width greater than 100 mm.

Although the high rib pitch to interspoke spacing of these silver halidecassettes (about 2.5-6.5%) is ideal for allowing photographic processingliquids to penetrate the spaces between the turns of the spirally woundphotographic film, such a high pitch-to-interspoke spacing ratio is veryinefficient for processing industrial rolls of film for anultra-barrier. Only a short length of film is able to be carried on acassette with such a high rib-pitch-to-interspoke spacing.

Fabrication of metal wire cassettes and low temperature plasticcassettes wider than 100 mm has proven to be difficult since smallvariations in winding/welding the wire or flow lines in injectionmolding the plastic cassettes cause distortion of the end plates. Thesestructural distortions would make a film difficult to load. The filmwould also have a tendency to fall out of the spiral grooves.

Although the metal wire cassettes can take the harsher processingconditions of vapor deposition, their symmetric rib geometry (aspectration of 1:1) isn't wide enough to hold the film as it expands fromroom to processing temperatures, especially for rib pitches less thanabout 6 mm. The plastic cassettes distort at the harsher processingconditions of vapor deposition, which are well above the heat deflectiontemperature of the plastic. In addition the self-threading feature ofsome plastic cassettes creates debris as a film substrate slides alongthe soft plastic ribs of the cassette.

Accordingly, in view of the foregoing, it is believed advantageous toprovide a film cassette that is able to edgewise support a spirallywrapped industrial length roll of a film substrate during a vapordeposition process in a way that minimizes scratching of the filmsurface during processing and which minimizes risk of creasing orcracking of the film or coating during loading and unloading, thusenabling the manufacture of an industrial length ultra-barrier film.

SUMMARY OF THE INVENTION

In one aspect the present invention is directed to a cassette forsupporting a length of a film substrate during a gaseous vapordeposition process. The cassette comprises a central shaft having afirst and a second end plate mounted thereon. Each end plate comprises acentral hub from which radiate a plurality of angularly spaced spokes.The spokes have an interior surface that lies on a reference planeoriented substantially perpendicular to the axis of the shaft. Theinterior surfaces of spokes are confrontationally disposed and spacedapart by a predetermined interspoke spacing defined between thereference planes.

Each end plate has a spiral rib mounted to the interior surface of thespokes thereon. Each spiral rib has a predetermined number of uniformlyspaced turns and a predetermined pitch associated therewith. The spacesbetween adjacent turns of the spiral rib define a spiral groove on eachend plate able to accept an edge of a film.

Each rib has a cross sectional configuration in a radial planecontaining the axis of the shaft. The cross sectional configuration hassubstantially linear major edges. Each rib exhibits a predeterminedwidth dimension, a predetermined average thickness dimension, and awidth-to-thickness aspect ratio of at least 2:1. In one embodiment thecross sectional configuration of the rib is substantially rectangularand may additionally include a flow spoiler at the free end thereof. Inan alternate embodiment the cross sectional configuration of each rib issubstantially wedge-shaped.

The interspoke spacing is at least three hundred millimeters (300 mm)and is also greater than the width dimension exhibited by a filmsubstrate at a gaseous deposition temperature. The width dimension ofthe rib on each end plate is between about 0.5% to about 2.0% of theinterspoke spacing.

In other aspects the present invention is directed to a cassette loadedwith a predetermined length of a film substrate and to a vapordeposition apparatus having an insert within which a loaded cassette isreceived.

In still other aspects the present invention is directed to an apparatusand to a method for loading a film cassette and to an apparatus and to amethod for unloading a film cassette and immediately laminating it to aprotective cover sheet.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the following detaileddescription taken in connection with the accompanying Figures, whichform a part of this application, and in which:

FIG. 1 is a stylized diagrammatic illustration of an apparatus forcoating a film substrate using a gaseous fluid vapor deposition processthat utilizes a film cassette in accordance with the present invention;

FIG. 2 is an elevation view of an optional diffuser plate used in thevapor deposition apparatus of FIG. 1;

FIG. 3 is a section view taken along section lines 3-3 of FIGS. 1 and 4showing a film cassette in accordance with the present invention forsupporting a length of a film substrate during exposure to a gaseousfluid;

FIG. 4 is an elevation view taken along view lines 4-4 in FIG. 3;

FIG. 5 is a section view taken along section lines 5-5 in FIG. 4 showingthe edges of a film substrate as received by the cassette and alsoillustrating the flow of vapor through the diffuser plate and into theflow passages defined between adjacent turns of the film substrate asthe same is supported by the cassette;

FIG. 6 is a section view generally similar to FIG. 5 showing therelative positions between the edges of a film substrate as received bythe cassette during a vapor deposition process and as the finishedsubstrate is removed from the cassette;

FIGS. 7A and 7B are section views showing alternate cross sectionalconfigurations for the rib of the film cassette;

FIGS. 8A and 8B are diagrammatic views showing the steps of a method inaccordance with the invention for manufacturing an end plate for acassette and a cassette comprising two end plates;

FIGS. 9A, 9B and 9C are diagrammatic views showing an apparatus inaccordance with the present invention for loading a film cassette; and

FIG. 10 is a diagrammatic view showing an apparatus in accordance withthe present invention for unloading a film cassette and immediatelylaminating it to a protective cover sheet.

DETAILED DESCRIPTION OF THE INVENTION

Throughout the following detailed description similar reference numeralsrefer to similar elements in all figures of the drawings.

FIG. 1 is a stylized diagrammatic illustration of an insert inaccordance with the present invention (generally indicated by referencecharacter 10) for coating a predetermined continuous length of a filmsubstrate F with one or more materials using a gaseous fluid vapordeposition process. The film substrate F in roll form is illustrated inthe Figures as being supported within the insert 10 by a cassette 100also in accordance with the present invention.

The insert 10 is useful within a gaseous vapor deposition apparatus forfabricating an industrial lengths of an ultra-barrier film, i.e., a filmhaving a water vapor transmission rate of less than 5×10⁻⁴ g-H₂O/m²-day.The ultra-barrier film is itself useful to protect the radiationcollection surface of a photovoltaic module. To manufacture such anultra-barrier film a transparent material (such as alumina Al₂O₃) isdeposited on both surfaces of a polymeric film substrate using a processsuch as atomic layer deposition. The gaseous deposition temperature foratomic layer deposition of alumina Al₂O₃ on polyethylene terephthalate(PET) is in the range from about 80 to 120 degrees Centigrade.

An industrial roll of film substrate F (that is, a film roll able to beused in an industrial scale process for the manufacture of photovoltaicmodules) should have a minimum length on the order of ten to two hundredmeters or more (10 to 200 m). Preferably the film F has a thickness inthe range from about 0.002 inches to about 0.010 inches (about 0.05 toabout 0.25 millimeters) and more preferably on the order of 0.005 inches(0.13 millimeters). The film substrate F for such a use may have apredetermined nominal width dimension W (i.e., a width dimension at roomtemperature) in a range from at least three hundred millimeters (300 mm)to about sixteen hundred fifty millimeters (1650 mm). It is alsoappreciated that the width dimension of the substrate F may grow on theorder of 0.4 to 0.6 percent due to thermal effects during the depositionprocess.

As diagrammatically suggested in FIGS. 1 and 3 and as will be developedherein, the structural features of the cassette 100 are sized andarranged such that when the film substrate F is edgewise supported bythe cassette 100 adjacent turns T of the spirally wrapped roll of film Fdefine an open (i.e., unobstructed) fluid conduction channel C throughwhich a gaseous vapor is able to propagate. Such an unobstructed channelis vital to insuring that a coating is deposited on both surfaces of thefilm without discontinuities being formed.

It is also important to prevent bending, surface abrasion and/or theimposition of other forces that may cause creases or cracks to developon the film and/or the coating while the film is loaded and unloadedfrom the cassette. Such abrasion, creases or cracks (even a crack ofnanometer dimension) may vitiate the protective effect of theultra-barrier deposited by the vapor deposition process. The size andarrangement of the structural features of the cassette 100 in accordancewith the present invention are also selected with this end in mind.

As diagrammatically illustrated in FIG. 1 an insert 10 for use with agaseous vapor deposition apparatus includes a pressure vessel 12 havinga process fluid inlet port 14 and a process fluid outlet port 16. Asuitable atomic layer deposition apparatus with which the insert 10 maybe used is that apparatus known as “Planar 400” or “Planar 800”available from Planar Systems Inc., Hillsboro, Oreg.

A diverging flow director 18 is connected to the process fluid inletport 14. The diverging flow director 18 serves to direct and todistribute uniformly a laminar flow of gaseous fluid toward a first endplate 106-1 of the cassette 100, as indicated by the flow arrow 26. Thediverging flow director 18 is contacted against or lies within apredetermined close distance of the exterior surface of the end plate106-1.

A converging flow director 28 may be disposed within the insert 10adjacent to the end plate 106-2 disposed at the opposite end of thecassette 100. The converging flow director 28 serves to conducts vaporemanating from the end plate 106-2 to the outlet port 16, as illustratedby the flow arrow 30. Preferably, the converging flow director 28 iscontacted against or lies a predetermined close distance to the exteriorsurface of the end plate 106-2.

In the embodiment illustrated the diverging flow director 18 includes anoptional diffuser plate 22 that is facially engaged against or withinthe close distance of the end plate 106-1. The diffuser plate 22 isshown in elevation in FIG. 2 and includes a plurality of openings 22Parranged in a spiral configuration. The plate may be manufactured from amaterial having a coefficient of thermal expansion similar to alumina,such as aluminum or titanium.

FIG. 3 illustrates a side elevation view, entirely in section, of thefilm cassette 100. The cassette 100 comprises a central shaft 102 ontowhich are mounted the first end plate 106-1 and the second end plate106-2.

In the embodiment illustrated each end plate 106-1, 106-2 is a generallycircular member comprising a central hub 106H from which radiate aplurality of angularly spaced spokes 106S. The radially outer ends ofthe spokes 102S may be connected by an outer rim 106M. The shaft 102extends through the openings in each of the hubs 106H. Once positionedthe hubs 106H are conveniently secured to the shaft 102, as by adhesiveor a fastener 108. Preferably the position of each end plate 106-1,106-2 along the shaft 102 is adjustably selectable.

The shaft 102 is an elongated hollow member having first and second ends102A, 102B thereon and a reference axis 102R extending therethrough. Theshaft 102 is preferably fabricated of aluminum or titanium, although anyother suitably rigid metallic or polymeric material able to withstandthe processing temperature may be used. The surface of the shaft 102 isinterrupted by a slot 102S that extends a predetermined distance 102Dalong the length of the shaft. The slot 102S is parallel to thereference axis 102R.

The rim 106M and each of the spokes 106S have thereon an exteriorsurface 106E_(M) and 106E_(S), respectively, and an interior surface106I_(M) and 106I_(S), respectively. The exterior surface 106E_(M) ofthe rim 106M serves as a convenient surface against which the divergingflow director 18 and the converging flow director (if provided) maycontact.

The interior surfaces 106I_(M) and 106I_(S) of the rim and spokes oneach end plate are confrontationally disposed with respect to the eachother. In the embodiment illustrated the interior surfaces 106I_(M),106I_(S) of each end plate 106-1, 106-2 lie on a respective referenceplane 112-1, 112-2. Each end plate 106-1, 106-2 has a spiral rib 106Rmounted to at least the interior surface 106I_(S) of the spokes 106S.The interior surface 106I_(M) of the rim 106M may be offset from thereference plane 112-1, 112-2, as the case may be, so long as the surface106I_(M) of the rim does not extend inwardly beyond the end of ribs106R. The reference planes 112-1, 112-2 are oriented substantiallyperpendicular to the axis 102R of the shaft 102.

With the end plates 106-1, 106-2 secured at a desired position on theshaft 102 a predetermined axial interspoke spacing 114 is definedbetween the confronting reference planes 112-1, 112-2. Once the cassetteis configured to exhibit a desired predetermined interspoke spacing 114between the end plates, the hubs and shaft should be secured such thatthe interspoke spacing 114 does not vary by more than one-quarter tothree millimeters (0.25-3 mm) around the perimeter of the end plates.

The outer diameter of the shaft 102 should be radially equal to theouter diameter of the hubs 106H of the end plates 106-1, 106-2 so thatthe hubs and shaft present a radially uniform surface between the endplates. To this end the shaft 102 in the embodiment illustrated has asleeve 110 disposed on the shaft 102 between the confronting referenceplanes 112-1, 112-2. The sleeve 100 has the same outer diameter as thatof the hub 106H. The sleeve 110 is provided a slot that registers withthe slot 102S in the shaft 102.

As noted each end plate 106-1, 106-2 has a spiral rib 106R mounted to atleast the interior surface 106I_(S) of the spokes 106S. A portion of therib may also be mounted to the interior surface 106I_(M) of the rim106M. The spiral rib 106R on each end plate 106-1, 106-2 has apredetermined number of uniformly spaced turns having a predeterminedpitch dimension 116. The pitch dimension 116 is measured at a givenangular position on an end plate in a radial direction with respect tothe axis 102R of the shaft 102. For example, the pitch dimension 116 maybe taken between the centers of adjacent turns of the spiral rib.

The open spacing 118 between adjacent turns of the spiral rib 106Rdefine a continuous spiral groove 106G on each end plate 106-1, 106-2.The groove 106G has a first, outer, end 106F and a second, inner, end106N (FIG. 4). The spiral grooves 106G on the end plates are arrangedsuch that the first and second ends 106F, 106N of each respective grooveaxially align.

Each rib 106R has a cross sectional configuration in a radial planecontaining the axis of the shaft. Generally speaking, the crosssectional configuration of the rib 106R exhibits substantially linearmajor edges, as perhaps best illustrated in FIGS. 5, 7A, 7B. The rib106R on each end plate has a predetermined width dimension 106W and apredetermined average thickness dimension 106T. The width dimension 106Wis measured from the interior surface 106I_(S) of the spokes 106S onwhich the rib 106R is mounted (i.e., from the reference plane 112-1,112-2) to the free end of the rib and is taken in a direction parallelto the axis of the shaft. The predetermined minimum thickness dimension106T is measured in a radial direction with respect to the axis of theshaft 102. The average thickness dimension is the average of thethickness dimensions of the rib taken at a predetermined number ofpoints across the width of the rib. In accordance with the presentinvention the rib has a width-to-average-thickness aspect ratio of atleast 2:1.

In the embodiment of the invention shown in FIGS. 3 through 6 each rib106R has a substantially rectangular cross sectional configuration. Bysubstantially rectangular it is meant that the major edges of the crosssectional configuration of the rib are substantially parallel to eachother along substantially the entire width and the thickness dimension106T of the rib is substantially uniform throughout substantially theentire width of the rib. If desired the free end of the rib may haverounded edges.

A modified embodiment of a rib having a substantially rectangular crosssection is shown in FIG. 7A. Such a modified rib includes a flow spoiler106P disposed at the free end thereof. The purpose of the flow spoiler106P is discussed in detail herein.

A rib in accordance with the present invention may also be configured toexhibit a substantially wedge-shaped cross sectional configuration 106D.Such an alternately configured embodiment of the rib is shown anddiscussed in connection with FIG. 7B.

As alluded to above, in accordance with the present invention, variousstructural features of the cassette 100 are sized and arranged toexhibit dimensions within the following ranges.

The interspoke spacing 114 is at least as large as the nominal widthdimension of the film substrate being supported by the cassette. Thus,generally speaking, a cassette in accordance with the present inventionhas an interspoke spacing 114 that is at least about three hundredmillimeters (300 mm).

In addition, the interspoke spacing 114 is also greater than the widthdimension exhibited by a film substrate F at a gaseous depositiontemperature so that, when the substrate F is received on the cassette, aclearance distance 106C (FIG. 3) is defined between the edge of thesubstrate F and the interior surface of the spoke.

The width dimension 106W of the rib 106R on each end plate is alsoimportant. As shown by the following Table 1, in accordance with thepresent invention the width dimension 106W should be in the range fromabout 0.5% to about 2.0% of the interspoke spacing.

TABLE 1 Film Width Interspoke Width Percentage of (mm) Spacing (mm) ofRib (mm) Interspoke Spacing 350 At least 350   2-6.5 0.57-1.86% 700 Atleast 700 4-8 0.57-1.14% 1000 At least 1000  6-12 0.60-1.20% 1350 Atleast 1350  8-16 0.59-1.18% 1650 At least 1650 10-20 0.60-1.20%

The effect of configuring a cassette having a rib width 106W and aninterspoke spacing 114 within the above-defined ranges may be understoodfrom FIGS. 5 and 6.

As suggested in FIG. 6, a cassette having ribs 106R with a widthdimension 106W within the defined range insures that a film substrate Fhaving a given stiffness when received within the spiral groove 106Gwill be edgewise supported and will not sag or otherwise obstruct thefluid conduction channel C defined between adjacent turns T of the filmF. The free outer end of a film roll having a film width greater thanabout 500 mm may require the support provided by an axially extendingstiffener V (FIG. 3).

The clearance distance 106C accommodates any enlargement to the film'swidth dimension owing to thermal expansion during processing of the filmat the process temperature. Providing edgewise support to the film alsominimizes the possibility of the film being touched by operator, whichmay leave unwanted organic matter on the surface of the film. Edgewisesupport of the film may minimize damage/debris and yield loss to film.

The flow path of vapor through a cassette 100 in accordance with thepresent invention is best illustrated in FIG. 5. It is noted that owingto the stiffness of the film F it is possible that the edge of the filmmay not be in contact with the same surface of a rib throughout the fulllength of the film. Thus, as suggested in FIG. 5, an edge of the film Fmay contact either the radially inner or radially outer surface of therib, or may reside in the spacing between adjacent turns of the rib.

Presently, a gaseous vapor deposition apparatus relies upon a diffusionmechanism to transport a gaseous fluid into contact with the surfacebeing coated. However, diffusion based processing requires relativelylong cycle times to coat one layer on the film. Coating cycle time isable to be reduced using an insert 10 of the present invention.

As discussed in connection with FIG. 1 the insert 10 includes adiverging flow director 18 having a diffuser plate 22 disposed in facialcontact against or within a close distance of the end plate 106-1. Asshown by the flow arrows in FIG. 5 the presence of the diverging flowdirector 18 serves to direct and to distribute uniformly a laminar flow26 of gaseous fluid toward the passages 22P in the diffuser plate 22.The laminar flow of process gas is accelerated as it is forced throughthe passages 22P and transitions to turbulent flow as it exits the plateand enters the space (defined by the axial dimension of the spokes)extant between the diffuser plate 22 and rib 106R. The conversion fromlaminar to turbulent flow is indicated by the fanned array of flowarrows 27. It is this turbulent flow 27 of gas that is conducted throughthe spaced openings 118 defining the spiral groove in the end plate106-1 toward the flow channel C formed between adjacent turns T of thefilm F. By disposing the plate 22 in contacting relationship with theend plate 106-1 (or within a close distance thereof) gas leakage isminimized.

Thus, when using a diverging flow director 18 in conjunction with adiffuser plate 22 the gas flows into the space between the ribs 118 andinto the channel C with both a radial as well as an axial flowcomponent, as indicated by the flow arrows 28. The radial component offlow into the flow channel C is needed to bring the precursors carriedin the gas into direct contact with the substrate. Since only a verysmall percentage of the precursor gasses actually absorb to thesubstrate when they impact it, a radial component of the flow isrequired to increase the chances of absorbing, thus making the flowthrough the channel C more efficient and reducing the overall cycle timefor an adequate ultra-barrier layer to develop. It is noted that asolely laminar flow will cause most of the precursors to travel thelength of the flow channel without significant impingement on thesubstrate, reducing overall coating efficiency.

A diffuser plate 22 may be omitted if a modified rib configuration asshown in FIGS. 7A or 7B is utilized on the end plate 106-1. When the rib106R is configured as shown in these figures a laminar flow from theflow director 18 is converted into a turbulent flow as it enters thechannel C. The conversion is effected either by the flow spoiler 106P(FIG. 7A) or by the wedge-shape 106D (FIG. 7B) of the rib.

An interspoke spacing 114 in the defined range additionally enables thefilm to be inserted into the groove without undue bending of the filmsurface. This is illustrated in FIG. 6. This means that the risk ofcreases or cracks forming on the film as it is loaded into the cassetteor the risk that a coating on the substrate will be cracked when thefilm is unloaded from the cassette are both minimized.

In sum, by sizing a cassette in accordance with the present inventionthe interspoke spacing 114 and the rib width 106W are both wide-enoughto edgewise support the film as it expands through the full temperaturerange of process temperatures without sag, yet narrow-enough to minimizefilm compression as the film is inserted and removed from the cassette,thus reducing creasing or cracking.

The capacity of the cassette in terms of the length of the roll of filmable to be supported thereby is governed by the pitch dimension and thethickness dimension of the rib 106R. Ribs are as thin as possible topermit maximum gaseous fluid flow and maximum loaded film length yetadequately strong so as not to break while loading or unloading.

The relationship between rib pitch and film length is tabulated in Table2.

TABLE 2 Cassette OD Length of Film Length of Film mm @ 3 mm Rib Pitch @1 mm Rib Pitch 200  9 m  27 m 350 31 m  92 m 600 64 m 191 m 700 127 m 380 m

The relationship of the rib pitch to the interspoke spacing is set forthin Table 3. In general, the pitch of each spiral rib is less than about1.2% of the interspoke spacing, and more preferably, is less than about0.5% of the interspoke spacing. The dimension 106T of the rib 106R oneach end plate is less than about fifty percent of the pitch. As theinterspoke spacing increases to accommodate wider film, the pitch of therib, and thus, the radial dimension of the channel C should be increasedproportionally to maintain the same flow resistance of the channel C.

TABLE 3 Film Width Interspoke Pitch Percentage of (mm) Spacing (mm) ofRib (mm) Interspoke Spacing 350 At least 350 1-4 0.28-1.14% 700 At least700 1-5 0.14-0.71% 1000 At least 1000 1-6 0.10-0.60% 1350 At least 13501-7 0.07-0.51% 1650 At least 1650 1-8 0.06-0.47%

As discussed, when the roll of film F is spirally wrapped on thecassette 100 the spaces between adjacent turns of the film cooperate todefine the gas flow channel C extending axially across the cassettebetween the end plates. As best seen in FIGS. 4 and 5 the portions ofeach spiral groove 106G exposed between angularly adjacent spokes 106Son each end plate define the plurality of openings 118 for the ingressor egress of the gaseous fluid into the gas flow channel C. The angulardimension of the spokes 106S is selected such that the areal extent ofthe exposed portions of the grooves (i.e., the total area of theopenings 118) is at least fifty percent of the predetermined area of theend plate.

The cassette 100 may be manufactured from a high temperature polymericmaterial such as a polycarbonate, liquid crystals, polyimid, acetalcopolymer, Nylon 6, polypropylene and PEEK. The cassette may also befabricated from a metal or ceramic.

Scraping between the film and the cassette could lead to debrisgeneration within the cassette. The debris could be generated byabrasion of the film and/or abrasion of the material of the cassette.

This debris could degrade the properties of a coating being formed onthe film. To minimize such scraping and debris generation at least thespiral rib 106R on each end plate is coated with a hard,abrasion-resistant layer 120 of a suitable ceramic or other protectivematerial. The thickness of the coating 120 lies in the range from about100 to about 2000 angstroms.

The coating material such as Al₂O₃, TiO₂, ZrO₂, HfO₂, and SiO₂ may beapplied using an atomic layer deposition process. A coating of SiN orSiC may be applied by a chemical vapor deposition process. If thecoating is alumina the coating thickness lies in the range from about100 to about 1000 angstroms.

The coating has a predetermined surface roughness less than about fiftymicrons (50 microns) and a hardness greater than Shore D 30. In thepreferred case, the coating is provided over the surface of the entireend plate.

-o-0-o-

Another aspect the present invention is directed to a process to make anend plate (e.g., end plate 106-1, 106-2) of a cassette in accordancewith the invention able to support a length of film during exposure to agaseous fluid at a temperature of 80 degrees centigrade or greater. Theend plates and the cassette made from two end plates are particularlyuseful in a process for atomic layer deposition of an inorganic coatingon polymer films.

As described above the end plate comprises a central hub 106H, an outerrim 106M and a rib 106R. The central hub 106H and the outer rim 106R areconnected by spaced spokes 106S. The rib is in the form of a spiralextending from the central hub to near the outer rim. The rib is mountedagainst interior surface of the spaced spokes and has a spiral end nearthe outer rim.

The end plate is formed from polymeric material such as a polycarbonate,liquid crystals, polyimid, acetal copolymer, Nylon 6, polypropylene andPEEK. Since the coating processes for which the end plate may be usedoperate at temperatures of 80 degrees centigrade or greater, the polymershould be appropriate for service at these temperatures. The selectedpolymer should have a heat distortion temperature at low pressure above80 degrees centigrade.

The process for making the end plate is shown schematically in FIG. 8A.The first step in the process is forming the uncoated end plate. Forexample a filament 202 emanating from a forming apparatus 203 isdeposited onto a baseplate 201 to begin the build-up of the end plate.The end plate may be formed by known techniques such as rapidprototyping, powder sintering, injection molding or laserpolymerization. In rapid prototyping, a prototyping machine reads datafrom a CAD drawing and lays down successive layers of liquid, powder,filament or sheet material to build up an object such as an end plate.In powder sintering, powder is injected into a mould and consolidated byheating. In injection molding, molten polymer is injected into a mould.In laser polymerization, a laser beam is irradiated in a pattern todeposit polymer from a vapor. For example, a fused deposition modelingapparatus available from Stratasys, Inc., Eden Prairie, Minn. asStratasys “Vantage” model FDM may be used.

In an optional second step as shown in FIG. 8A the end plate is heattreated to reduce residual stresses. In the Figure, the end plate 106-1,106-2 is located in a furnace 204. An industry standard (Blue-M)convection oven may be used.

Appropriate heat treating temperatures are at least twenty degrees abovethe temperature of inorganic coating deposition process in which the endplate may be used. For example, an atomic layer deposition process usedto form an ultra-barrier operates at a minimum of 80 degrees centigrade.Accordingly, the heat treating temperature for such an end plate wouldbe a minimum of 100 degrees centigrade.

The next step in the process is coating the polymer end plate with aninorganic coating such as alumina, silicon nitride, silicon carbide,TiO₂, ZrO₂, HfO₂, and SiO₂. If the coating is alumina the coatingthickness lies in the range from about 100 to about 1000 angstroms.

This is shown schematically in FIG. 8A. The end plate 106-1, 106-2 isplaced in a coating apparatus 205. This coating is used to smooth andharden the surface of the polymer end plate so that debris is notgenerated from wear of the end plate when a length of film is loaded orunloaded into the cassette. The surface roughness of the inorganiccoating should be less than about fifty microns (50 microns) and thehardness of the inorganic coating should be greater than 30 on the ShoreD scale. Debris may create defects in a coating applied to the film inthe cassette. The coating system 205 may effect known techniques such aschemical vapor deposition, physical vapor deposition, or plasmadeposition used for deposition of the inorganic coating on the endplate. The thickness of the coating may be 100 to 2000 angstroms,preferably 100 to 1000 angstroms for alumina. The coating may bedeposited using a Planar P-400A atomic layer deposition platform.

Another aspect of the invention is a process to make a cassette (e.g., acassette 100) for supporting a length of film during exposure to agaseous fluid having a temperature 80 degrees centigrade or greater. Thecassette 100 comprises two end plates which are each made as in theprocess described above. The process of making the cassette furthercomprises the steps of mounting each end plate 106-1, 106-2 near eachend 102A, 102B of a central shaft 102 as shown in FIG. 8B. The centralshaft 102 may also be fabricated of a metal or the same polymers as theend plates. A hole in the central hub of the end plates may be sized tofit closely with the diameter of the central shaft. The end plates aremounted near the ends of the central shaft as shown in FIG. 8B.

The next step in the process of making the cassette, shown in FIG. 8B,is aligning the spiral ends of the rib 106R. The spiral ends 106F of thegroove for both of the end plates should be located at the same axialposition relative to the central shaft. This is necessary to accommodateloading and unloading of film into the space inside the spirals of therib. One of the end plates is rotated about the shaft until the spiralends are aligned. After aligning the spiral ends of the ribs the endplates may be secured to the central shaft by fastener 108 (such as aset screw) or adhesive. The central shaft may be slotted in secure theend of a film to facilitate loading of the film into the cassette. Thedimensions of the slot in the central shaft may be may be in the rangefrom about one hundred to about fifteen hundred fifty millimeters (100to 1550 mm).

-o-O-o-

Another aspect of the present invention is an apparatus and method forloading a film cassette 100 for a gaseous vapor deposition process. Theapparatus is shown in FIGS. 9A, 9B, and 9C.

The apparatus comprises a unloaded cassette 100 for supporting a lengthof a film F during a gaseous vapor deposition process as describedabove. The unloaded cassette 100 itself comprises a central shaft 102having an axis 102R. The shaft comprises an axially extending slot 102S.The unloaded cassette 100 also comprises a first and a second end plate106-1, 106-2 mounted to the shaft 102. Each end plate 106-1, 106-2 has aspiral groove 106G. The spiral grooves 106G in each end plate areaxially aligned. The end plates 106-1, 106-2 are spaced apart by apredetermined interspoke spacing 114. The cassette is mounted in acassette mounting stand 301 which allows the cassette to rotate freelyabout the axis 102R of the central shaft. The cassette mounting stand301 can be adjusted for lateral alignment. Examples of techniques forlateral alignment adjustment may be insertion of washers or o-rings onthe shaft 102. Lateral alignment moves the edges of the end plates ofthe unloaded cassette relative to a reference plane 306. The centerpoints of a supply roll 303 and the shaft 102 of the cassette should bealigned within about 3 millimeters on a reference plane 306perpendicular to both axes and passing through both center points. Theapparatus also comprises a supply roll mounting stand 302 supporting thesupply roll of film 303. The supply roll 303 has an axis 304. The axisof the supply roll 304 is spaced a predetermined distance from the axisof the unloaded cassette 102R. The distance between the axis of thesupply roll 304 and the axis of the unloaded cassette 102R is selectedaccording to the width of the film F being coated. The distance betweenthe axes of the supply roll 303 and the unloaded cassette 100 should bebetween about 0.25 and 3 times the width of the film F.

The cassette mounting stand 301 and the supply roll mounting stand 302both have axes. These axes should be parallel with 0.5 degrees in thetram (x-direction) and level (z-direction). Potential misalignment inthe tram direction of the axes 304, 305 is shown in FIG. 9B. Potentialmisalignment in the level direction of the axes 304, 308 is shown inFIG. 9C. The mounting stands may comprise mechanical mechanisms toadjust the parallelism of the axes.

Examples of mechanical mechanisms to adjust the parallelism of the axesinclude leveling screws, jacking bolts, and shims.

The stands 301, 302 could themselves be mounted to a base plate 300, ifdesired.

The film F is taken from the top of the supply roll 303 and enters theunloaded cassette 100 at the bottom as shown in FIG. 9A. The leadingedge of the film is tapered and inserted into the slot 102S on the shaft102 of the unloaded cassette 100.

A tensioning device 307 is connected to the supply roll of film 303.During film loading into the cassette, the film F is tensioned such thatthe edges of the supply film remain captured within the spiral groovesin both end plates without producing creasing in the surface of the filmas the film is wound onto the cassette. Examples of tensioning devicesinclude pony brakes, pneumatic brakes, magnetic particle clutches,caliper brakes and drum brakes. Dynamic tensioning can also be used. Thetensioning device 307 must be capable of smoothly tensioning the film Fin a range from about 0.02 to 0.36 Newtons per millimeter of film width.

The present invention is further directed to a process for loading afilm cassette for a gaseous vapor deposition process. To eliminatescratching of the film F, traditional film alignment and tensioningtechniques which use rolls contacting the film cannot be used. Inaddition, this process requires tighter specifications on alignment inparallelism and allowable offset distance than traditional web handlingprocesses. Both of these requirements must be satisfied in order toavoid scratching or creasing the film F.

The first step in the process is mounting a supply roll 303 of a film ona first mounting stand 302. The supply roll of the film 303 has atapered free end. The supply roll having a axis 304 and a referenceplane 306 perpendicular to the axis 304 and passing through the centerpoint of the supply roll.

The next step in the process is mounting an unloaded film cassette 100on a second mounting stand spaced a predetermined distance 309 from thefirst mounting stand. The unloaded film cassette having an axis 102R anda central reference plane 306 perpendicular to the axis and passingthrough the center point of the unloaded cassette. The unloaded cassettecomprises a central shaft 102 having an axially extending slot 102S. Theunloaded cassette also comprises a first 106-1 and a second 106-2 endplate mounted to the shaft 102. Each end plate has a spiral groove 102G.The spiral grooves 102G in each end plate are axially aligned. The endplates are spaced apart by a predetermined interspoke spacing 114. Themounted supply roll and the mounted cassette can be seen in FIGS. 9A and9B.

The third step in the process is inserting the tapered free end of thefilm F into the slot 102R in the central shaft 102 of the unloadedcassette 100. The film F should follow a path from the top of the supplyroll 303 to bottom of the cassette 100, as shown in FIG. 9A. The lengthof the taper from the free end of the film to the untapered (i.e., fullwidth) portion of the film should be fifteen to twenty centimeters. Theangle between the edge of the untapered and the tapered edged should bein the range of fifteen to thirty degrees.

The fourth step in the process is aligning the central reference plane306 (shown in FIG. 9B) on each roll to within a predetermined allowableoffset distance. The allowable offset distance is the distance betweenplanes perpendicular the supply roll axis 304 and passing through thecenter point of the supply roll 303, and the unloaded cassette axis 102Rand the center point of the cassette shaft 102. The predeterminedallowable offset distance is about three millimeters. This alignment maybe accomplished by inserting washers, o-rings or shims between thesupply roll mounting stand 302 and the supply roll 303 and the cassettemounting stand 301 and the unloaded cassette 100.

The fifth step in the process is aligning the axis of the supply rolland the axis of the unloaded cassette within 0.5 degrees of parallelismwith respect to each other in both the tram (x direction) and in thelevel (z-direction). Alignment is illustrated FIGS. 9B and 9C. Thisalignment can be accomplished by adjusting level screws, jack bolts orshims associated with the mounting stands.

The sixth step in the process is imposing a predetermined tension intothe film. The tension is imparted by a tensioning device 307 located onthe supply roll 303. Examples of tensioning devices 307 include ponybrakes, magnetic particle clutches, caliper brakes and drum brakes.Dynamic tensioning can also be used. The film F is tensioned in a rangefrom about 0.02 to 0.36 Newtons per millimeter of film width.

The seventh step in the process is rotating the unloaded cassette 100with respect to the supply roll 303, drawing the film F into the spiralgrooves 102G in both end plates 106-1, 106-2 without producing creasingor scratching in the surface of the film F. The unloaded cassette may berotated manually as long as the film F is not touched.

For film widths greater than about 500 millimeters, the axiallyextending stiffener V (in FIG. 3) is inserted around the outward end ofthe film F in the now-loaded cassette. This stiffener minimizesunwinding of the film F from the cassette during handling and coatingdeposition.

-o-O-o-

Another aspect of the present invention is an apparatus and method forunloading a film cassette from a gaseous vapor deposition process andlaminating it to a protective film to minimize scratching of theultra-barrier coating. To eliminate scratching of the film F,traditional film alignment and tensioning techniques which use rollscontacting the film cannot be used. In order to protect the coated filmuntil lamination, an apparatus which avoids touching the filmultra-barrier coating U on one surface of the film is needed. Theapparatus is shown in FIG. 10.

The unloading apparatus comprises a cassette mounting stand 401supporting a loaded cassette 100 from a gaseous vapor depositionprocess. The loaded cassette 100 comprises a central shaft 102 having anaxially extending slot 102S. The loaded cassette 100 further comprises afirst 106-1 and a second 106-2 end plate mounted to the shaft 102. Eachend plate having a spiral groove 102G in it. The spiral grooves 102G ineach end plate are axially aligned. The end plates are spaced apart by apredetermined interspoke spacing 114. A coated film F is supported bythe spiral grooves 102G. The film has a free outer end. The loadedcassette further comprises a central shaft 102 having an axis 102R.

The unloading apparatus further comprises a tensioning device brake 402connected to the loaded cassette 100. The tensioning device is a activetensioning device such as magnetic particle brake, pneumatic brake or afriction brake. The tensioning device comprises a load cell 412. Such anintegrated tensioning device with a brake and a load cell may beobtained from Dover Flexo Electronics (Rochester, N.H.). The film shouldbe tensioned to between 0.175 to 0.50 Netwons per millimeter.

The unloading apparatus further comprises a mounting stand 403supporting a roll of protective film 404. The protective film has a freeend. The protective film may be any polymer which may be subsequentlylaminated with use of an adhesive at room temperature or above. For useas barrier layers in photovoltaic modules, a fluoropolymer protectivefilm such FEP, ETFE, and PFA is desirable. Fluoropolymer protectivefilms must be corona treated (Enercon Surface Treatment Inc, Germantown,Wis.) to be laminated.

The unloading apparatus further comprises nip rolls 406 into which thefree ends of the coated film F and the protective film 405 are insertedso that they form a laminate 407. The nip rolls 406 should be operatedat room temperature or above. The load on the nip rolls should begreater than 0.10 Newtons per millimeter of film width. The nip rollsand tensioning device should be operated to minimize curl of thelaminate.

The unloading apparatus further comprises a wind up roll 408 to collectthe laminate from the nip rolls.

The wind up roll 408 is connected to a wind up roll tension controldevice 409. The wind up tension control device may be load cellcontrolled as may be obtained from MagPowr Inc. (Oklahoma City, Okla.).The tension in the laminate 407 should be greater than 0.10 Newtons permillimeter of film width.

The unloading apparatus further comprises an adhesive coater 410 toapply a adhesive to the protective film 404 located between the roll ofprotective film 404 and the nip rolls 406. The adhesive coater may beslot-die coater, gravure coater, or a reverse gravure coater. The coatershould be appropriate to the adhesive selected for a given application.For a single side corona-treated FEP protective film laminated to analumina-coated PET substrate an adhesive available from national Starch,Bridgewater, N.J.) under the trademark Duro-Tak is used. A slot-diecoater is available from Egan Film and Coating Systems & Blow MoldingSystems, Somerville, N.J. The adhesive coater may also apply a solidadhesive to the protective film.

The unloading apparatus further comprises an optional drier 411 to drythe adhesive located between the adhesive coater and the laminator. Thedrying parameters depend on the adhesive selected.

The present invention is also directed to a process for unloading a filmcassette 100 for a gaseous vapor deposition process and laminating it toa protective film. The process description refers to FIG. 10. Dirt ordebris on the film contaminate this process. The process should beperformed in a clean room environment or a cleaner should be providedprior to the lamination step. The rolls in this process should bealigned as described above for the loading method including parallelismin the tram (x) direction and level (z) direction and lateral alignment,between the cassette nip rolls and all rolls therebetween.

The first step in the process is providing a loaded cassette 100 holdingcoated film F. The loaded cassette 100 comprises a central shaft 102having an axially extending slot 102S and a first 106-1 and a second106-2 end plate mounted to the shaft 102. Each end plate has a spiralgroove 102G in it. The spiral grooves 102G in each end plate are axiallyaligned. The end plates 106-1, 106-2 are spaced apart by a predeterminedinterspoke spacing 114. The coated film F is supported by the spiralgrooves 102G and has a free end. A sacrificial leader may be spliced tothe free end of the coated film to establish operating settings.

The next step in the process is providing a roll of protective film 404.The protective film 404 may be any polymer which may be nip laminated atroom temperature or above. For use as barrier layers in photovoltaicmodules, a fluoropolymer protective film such FEP, ETFE, and PFA isdesirable. Fluoropolymer protective films must be corona treated(Enercon Surface Treatment Inc, Germantown, Wis.) to be laminated.

The third step in the process is applying an adhesive to the protectivefilm to form an coated protective film. The adhesive is coated by anadhesive coater 410. The adhesive coater 410 may be slot-die coaters,gravure coaters, and reverse gravure coaters. The coater 410 should beappropriate to the adhesive selected for a given application. For asingle side corona-treated FEP protective film laminated to analumina-coated PET substrate, a durotac 80-1194 (National Starch,Bridgewater, N.J.) adhesive is used in conjunction with a slot-diecoater available from Egan Film and Coating Systems & Blow MoldingSystems.

Especially for fluoropolymers, a static eliminator should be used whereflammable solvents are present such as in the adhesive.

In a fourth step, the adhesive is dried in a drier 411. The dryingtemperature should be above about 60 degrees centigrade. Dryingconditions vary with the adhesive selected.

The fifth step in the process is laminating the coated film and thecoated protective film to form a laminate 407. This is done by feedingthe adhesive-coated protective film and the coated film into nip rolls406. The nip rolls 406 should be operated at room temperature or above.The load on the nip rolls 406 should be greater 0.10 Newtons permillimeter of film width. The nip rolls 406 (temperature and pressure)and tensioning device 412 should be operated to minimize curl of thelaminate for given materials selected. The curl of a laminate depends onthe adhesive, film substrate properties, protective film properties,temperature, pressure, and film tensions. One of ordinary skill in theart can determine the optimum process parameters for selected materials.

In the sixth step, the laminate is collected on a wind up roll 408. Thewind up roll 408 is controlled by a wind up roll tension control device409. The wind up tension control device 409 may be load cell controlledas may be obtained from MagPowr Inc. (Oklahoma City, Okla.). The tensionin the laminate 407 should be greater than 0.12 Newtons per millimeterof film width. There is an upper limit to the tension applied to thelaminate where the inorganic coating on the film substrate fractures.This limit depends on the inorganic coating material and its thickness.

Examples

The following Examples illustrate the results of the use of a cassettein accordance with the present invention to support a film substrateduring an atomic layer deposition process.

Example 1

Polyethylene terephthalate (PET), uncoated, plastic film, 0.005 inchesthick, obtained from DuPont Teijin Films, Hopewell, Va., was manuallyloaded on a spiral cassette as shown in FIGS. 3-6 with an inner diameterof about 62 mm and an outer diameter of about 200 mm. The cassette withspirally grooved end plates, fabricated from polycarbonate, had a pitchbetween the spiral grooves of 4.0 mm, and the width of the cassette wasabout 350 mm. The spacing between turns of the spiral rib (i.e., thespacing 118, FIG. 3, defining the radial width of the groove) was 2.5mm. The rib thickness was 1.5 millimeters and rib width was 6.5millimeters. The length of uncoated PET, fully wound on the cassettewith 4 mm pitch, was approximately 7 meters. This cassette with PET filmwas loaded into a reactor (Planar P400A) for depositing a thin filmcoating of an Al₂O₃ barrier layer on both sides of the PET by atomiclayer deposition (ALD). Prior to ALD deposition the temperature in theALD reactor was raised to 100° C. and held there for 3 hours prior toALD coating to remove any residual water absorbed by the PET plasticfilm.

For the ALD deposition of Al₂O₃ the reactor was maintained at 100° C.The reactants or precursors used for ALD deposition of Al₂O₃ weretrimethyl aluminum vapor and water vapor. These precursors wereintroduced sequentially into ALD reactor, which was continuously purgedwith a nitrogen gas and pumped with a mechanical pump to a backgroundpressure (no reactant or precursor) of about 1 Torr. The nitrogen gaswas used as a carrier for the reactants and also, as a purging gas. Morespecifically, the PET substrate was dosed with water vapor carried bynitrogen gas for 4 seconds, followed by purging of the reactor inflowing nitrogen for 20 seconds. The substrate was then dosed for 4seconds with trimethyl aluminum vapor carried by nitrogen gas, followedby a 20 second purge in flowing nitrogen. This reaction sequenceproduced a layer of Al₂O₃ on both sides of the PET substrate. Thereaction sequence was repeated 200 times, which formed an Al₂O₃ barrierlayer whose thickness was determined by optical ellipsometry to beapproximately 29 nm thick on both sides of the PET substrate, 7 metersin length.

To assess the permeation of water vapor through the ALD coated Al₂O₃film, coated on the cassette, the film was unrolled and 2 samples werecut (about 100 mm×100 mm) from the center of the 7 meter long PET.Additionally 2 samples (about 100 mm×100 mm) were cut that were coatednear the outer or larger diameter portion of the cassette. The watervapor transmission rate (WVTR) for all four samples was measured in acommercial instrument (MOCON Aquatran-1, Minneapolis, Minn.). Thisinstrument has a sensitivity for WVTR of 5×10⁻⁴ g-H₂O/m²-day. All foursamples tested below this limit. That is, their WVTR was less than5×10⁻⁴ g-H₂O/m²-day. This is consistent with a uniform and high qualitycoating of Al₂O₃ over the entire 4-mm pitch cassette.

Example 2

The experiment described in Example 1 was repeated with a cassette thathad a 2 mm pitch between spiral grooves. The rib thickness was 1.0millimeters and rib width was 6.5 millimeters. That is, the uncoated PETloaded on this cassette was 350 mm wide×about 14 meters in length.(i.e., the spacing 118, FIG. 3, defining the radial width of the groove)was 1.0 mm. The 2 mm-spiral with uncoated PET was loaded into the ALDreactor and heated in the ALD reactor at 100° C. to remove residualwater vapor absorbed by the PET, followed by ALD deposition of Al₂O₃ at100° C. on both sides of the PET. The ALD deposition process consistedof dosing with water vapor, carried by nitrogen gas, for 8 seconds,followed by purging of the reactor in flowing nitrogen for 50 seconds.The PET substrate on the 2 mm-pitch cassette was then dosed for 8seconds with trimethyl aluminum vapor carried by nitrogen gas, followedby a 50 second purge in flowing nitrogen. This reaction sequenceproduced a layer of Al₂O₃ on both sides of the PET substrate. Thereaction sequence was repeated 200 times, which formed an Al₂O₃ barrierlayer whose thickness was determined by optical ellipsometry to beapproximately 30 nm thick on both sides of the PET substrate, 14 metersin length.

The water vapor transmission rate (WVTR) was measured for four sampleson the ALD coated PET after unrolling it from the cassette. Two sampleswere measured from the middle of the unrolled PET and two samples weretaken from the PET coated at a location near the outer diameter of thespiral. All four measurements were below the sensitivity of the MOCONAquatran-1 instrument of 5×10⁻⁴ g-H₂O/m²-day. That is, their WVTR wasless than 5×10⁻⁴ g-H₂O/m²-day. This is consistent with a uniform andhigh quality coating of Al₂O₃ over the entire 2-mm pitch cassette.

These Examples demonstrate that use of a cassette, loaded and processedin a vapor deposition apparatus, all as described in accordance with thepresent invention, produced a superior barrier film having a water vaportransmission rate less than 5×10⁻⁴ g-H₂O/m²-day.

Those skilled in the art, having the benefit of the teachings of thepresent invention as hereinabove set forth may effect numerousmodifications thereto. Such modifications are to be construed as lyingwithin the contemplation of the present invention as defined by theappended claims.

1. A process for making the end plate of a cassette for supporting alength of film during exposure to a gaseous fluid having a temperature80 degrees centigrade or greater comprising the steps of: a) forming anend plate of polymer wherein the end plate comprises a central hub, anouter rim, and a rib, the hub and the outer rim being connected by aplurality of spaced spokes having an interior surface, the rib beingformed in a spiral fashion to the interior surface of the spokes; b)optionally, heat treating the end plate; and c) coating the end platewith an inorganic coating, the coating having a surface roughness lessthan about fifty microns (50 microns) and a hardness greater than ShoreD
 30. 2. The process of claim 1 wherein the polymer has a heatdistortion temperature at a load of 0.46 MPa above 80 degreescentigrade.
 3. The process of claim 1 wherein the polymer is selectedfrom the group consisting of polycarbonate, liquid crystals, polyimid,acetal copolymer, acrylic, Nylon 6, polyethylene, polypropylene andPEEK.
 4. The process of claim 1 wherein the forming of the end plate isby rapid prototyping, powder sintering, injection molding or laserpolymerization.
 5. The process of claim 1 wherein the inorganic coatingis alumina, silicon nitride, or silicon carbide.
 6. The process of claim1 wherein the coating of the inorganic coating is by chemical vapordeposition, physical vapor deposition, or plasma deposition.
 7. Theprocess of claim 1 wherein the central shaft is slotted.
 8. A processfor making a cassette for supporting a length of film during exposure toa gaseous fluid having a temperature 80 degrees centigrade or greatercomprising the steps of: a) forming two end plates of polymer whereinthe end plates each comprise a central hub, an outer rim, and a rib, thehub and the outer rim being connected by a plurality of spaced spokeshaving an interior surface, the rib being formed in a spiral fashion tothe interior surface of the spokes and the rib having an end of thespiral; b) optionally, heat treating the two end plates; c) coating theend plates with an inorganic coating, the coating having a surfaceroughness less than about fifty microns (50 microns) and a hardnessgreater than Shore D 30; d) mounting the end plates on both ends of acentral shaft having two ends such that the interior surface of thespokes face each other; and e) aligning the ribs of both end plates suchthat the end of the spiral on both end plates is at the same radialposition.
 9. The process of claim 8 wherein the polymer has a heatdistortion temperature at a load of 0.46 MPa above 80 degreescentigrade.
 10. The process of claim 8 wherein the polymer is selectedfrom the group consisting of polycarbonate, liquid crystals, polyimid,acetal copolymer, acrylic, Nylon 6, polyethylene, polypropylene andPEEK.
 11. The process of claim 8 wherein the forming of the end plate isby rapid prototyping, powder sintering, injection molding or laserpolymerization.
 12. The process of claim 8 wherein the inorganic coatingis alumina, silicon nitride, or silicon carbide.
 13. The process ofclaim 8 wherein the coating of the inorganic coating is by chemicalvapor deposition, physical vapor deposition, or plasma deposition. 14.The process of claim 8 wherein the central shaft is slotted.